1. Field of the Invention
The present invention generally relates to a multi-antenna system using a closed-loop scheme, and more particularly to a method for transmitting/receiving feedback information in a multi-antenna system supporting multiple users, and a feedback system supporting the same.
2. Description of the Related Art
In wireless channel environments, as opposed to wired channel environments, reliability may be low due to multipath interference, shadowing, propagation attenuation, time variant noise, interference, and the like. There is a problem in that a data transmission rate may not increase due to the low reliability in mobile communication environments.
To overcome these problems, a multiple-input multiple-output (MIMO) system has been proposed. The MIMO system is a representative example of a multi-antenna system.
The multi-antenna system supports a single-user mode and a multi-user mode. In the single-user mode, data is transmitted to the same user via multiple transmit antennas. In the multi-user mode, data is transmitted to multiple users via multiple transmit antennas.
The multi-antenna system is divided into a closed-loop scheme in which resource allocation depends on feedback information, and an open-loop scheme independent of the feedback information. To transmit the feedback information in the multi-antenna system using the closed-loop scheme, a full feedback scheme and a single feedback scheme are present.
When precoding is used, the full feedback scheme is a scheme in which each user feeds back information regarding all transmission rates mapped to all column vectors within a codebook. The full feedback scheme has superior performance in terms of resource allocation, but is disadvantageous since there is a large amount of feedback information. When the feedback information to be generated increases, not only system complexity may increase, but also an amount of resources required to transmit the feedback information may increase.
When precoding is used, the single feedback scheme is that in which each user feeds back only index information of a column vector having a highest transmission rate. The single feedback scheme may reduce an amount of feedback information. However, it is difficult to expect optimal resource allocation in the single feedback scheme.
In the multi-antenna system using the closed-loop scheme as described above, an important problem is to provide a scheme for efficiently allocating resources on the basis of minimum feedback information. In particular, it is urgent to provide a scheme for transmitting optimal feedback information while taking into consideration an operating mode, a feedback scheme, and the like, in the multi-antenna system.